Opinion: Brain science key in trial of alleged 'Batman' shooter

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Editor's Note: Dr. David Eagleman directs the Eagleman Laboratory for Perception and Action at Baylor College of Medicine in Houston. He is the subject of Sunday's episode of "The Next List," on CNN at 2 p.m. ET.

By David Eagleman, Special to CNN

(CNN) --- In the wake of the Aurora, Colorado, movie theater shooting, many people are asking the same questions: What kind of derangement is revealed by the alleged acts of James Holmes, who has been charged with murder and attempted murder in a massacre during a showing of "The Dark Knight Rises"? What is wrong with the brain that concocted this plot? How will information about Holmes' mental state play out in the courts?

My goal here is to bring a perspective on this tragedy from the point of view of a neuroscientist.

Few facts are publicly available about Holmes’ mental health background. Despite the dearth of data, however, several issues can be clarified and discussed.

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To begin, it’s critical to understand the difference between two words: psychotic and psychopathic. These are two similar-sounding terms that commentators sometimes use interchangeably.

But, in reality, they are entirely different.

A person with a psychosis is disconnected from reality. For example, a homeless person arguing with himself is typically suffering from a psychosis such as schizophrenia. Someone with this sort of mental illness is termed “psychotic.” A person with a disorder of mood such as bipolar disorder (in which one alternates between depression and mania) can also have associated psychotic features such as hallucinations and delusions.

In contrast, a person with psychopathy has low empathy and low remorse. The psychopath can be smart, glib, charming and blend in perfectly with the society around him, but he lacks compassion and guilt. Behind his “mask of sanity” lurks a manipulative creature who can hurt others without compunction. A psychopath (or, synonymously, a sociopath) is someone like Jeffrey Dahmer or Ted Bundy. They are termed “psychopathic”.

Which, if either of these, was Holmes? If convicted of the crimes, did he suffer from a psychosis, or was he instead a cognitively intact but emotionless sociopath? When Colorado Rep. Ed Perlmutter told the media that Holmes was “a psychotic son of a bitch," it’s safe to guess that his statement stemmed from a confounding of the terms rather than a specific diagnosis.

The facts about Holmes’ mental state are almost entirely under gag orders, so it is impossible to make a diagnosis at a distance. But my purpose here is to sketch the various scenarios which could happen in the courtroom.

First, if Holmes is found to verifiably suffer from a psychosis (especially with a historical medical record to back up the diagnosis), then his attorney likely will plead not guilty by reason of insanity. If the plea is successful, he would be committed to a mental health institution, presumably for life.

Historically, the public finds a successful insanity plea unsatisfying. However, even the ancient Greeks recognized that someone disconnected from reality cannot be treated the same way as someone with normally functioning cognition. In other words, when people are disconnected from reality as the product of a mental health disorder, moral blame traditionally does not attach itself to the person in the same way.

A recent New York Times article reported that Holmes felt he might have dysphoric mania, a term that describes the presence of depressive symptoms hand-in-hand with the elation, agitation and flight of ideas that characterize a manic state. (Dysphoric mania is sometimes called “mixed mania,” “depressive mania” or “agitated depression.”) This type of mania is commonly accompanied by psychosis, which would make it eligible for the insanity defense. It has not yet been made public whether Holmes was professionally diagnosed with a mixed mania or if instead he made the supposition himself.

It is of interest that Colorado is one of only a few states in which the burden of proof lies on the prosecution for an insanity defense. In other words, the state must establish from other clues that Holmes could indeed distinguish right from wrong and understood the nature and consequences of his alleged actions. This argument will be made from a careful examination of Holmes’ other behaviors around that time. A typical example of this sort of investigation looks at issues of whether he, for example, changed his behavior or hid his actions around authority figures. If so, that would be used to build a case that he understood the morality and effects of his choices.

Now let’s turn to another scenario: Suppose that instead of having a psychosis, Holmes had a psychopathy. In that case, he would not be able to plead insanity. For insanity defense purposes, one must have a mental illness, and psychopathy does not qualify. This is because psychopaths fully understand the nature and consequences of their crimes; they commit their acts simply because of a lack of compunction and remorse.

As more data emerge about Holmes’ past and present, the question of his mental condition will be clarified. Of course, his problem could be something other than psychosis or psychopathy.

One suspect in bizarre acts like this is the presence of drugs (specifically, psychoactive drugs, or those that affect the brain and can change cognition and behavior). But a drug-induced mental state seems less likely given his allegedly meticulous, months-long purchases of weapons, ammunition and explosives.

Another root of incomprehensible behavior can be a brain tumor, such as the small tumor that grew in the brain of Charles Whitman, the shooter in the 1966 University of Texas tower massacre. Let me be clear that I see a brain tumor as an extremely low probability explanation in Holmes’ case, but nothing should escape scrutiny in a case like this. In the unlikely event that Holmes has a tumor (and one which could be plausibly argued to have steered his behavior), this could serve as a mitigating factor during sentencing. Presumably, such a scenario would leave a bitter taste on the public tongue. On one hand, everyone would agree that a behavior-changing tumor would not be his fault. On the other hand, the direct link between brain and behavior tends to go underappreciated in powerful emotional winds, and the desire for punishment is understandably strong. Therefore, the discovery of a brain tumor would test our capacity to deal with such a horrific act in the light of modern biology.

One does not have to be an expert to surmise that something appears to be wrong with Holmes’ brain, but it makes a difference what that problem turns out to be. The answer navigates his possible outcomes in court.

The opinions expressed in this post are solely those of David Eagleman.